Refrigerated display cases which have a front opening portion are well known in the prior art. In the prior art, multiple air curtain construction is utilized in the display case to isolate the refrigerated space from the ambient atmosphere. In this way, the refrigerated foods or the like are easily removed from and replaced in the refrigerated display case. The display case employs an innermost air curtain and a second adjacent air curtain which are normally circulated within the display case through conduits provide therein. The innermost air curtain is normally the coldest and the second curtain is somewhat warmer. A refrigerating means, typically in the form of one or more evaporators, is located within the innermost curtain passage for cooling the air flow therethrough.
In this type of refrigerated display case, the innermost curtain passage and the refrigerating means must be frequently defrosted to remove the accumulated frost on the evaporators collected from the cooled air which impedes the operation of the equipment. On a commerical unit, such a defrosting operation is achieved by the use of electrical heaters located adjacent to the evaporator of the refrigerating means, or in some instances, by passing a hot gas through the evaporator of the refrigerating means. However, the hot gas defrost method is complex in its construction and is practical in only a small percentage of the installations. With the electrical heater defrost, the refrigerating mechanism is temporarily heated while allowing the circulating air through the air curtains. Thus, the circulating air is warmed by the high voltage electrical heater. The warm air can then melt the frost built up on the evaporator. It is important to melt this frost as rapidly as possible, in order to minimize the temperature rise of the refrigerated foods and to minimize collection of frost on the refrigerated foods from the higher humidity in the recirculated warm air.